In Computed Tomography (CT) imaging system, an accurate and collimating X-ray source and a high-sensitivity detector are employed for a series of tomographic scanning around a part of a human body. In the process of scanning, the X-ray beam attenuates when passing through the human body and the attenuated X-ray beam is received by the detector. Then, an analog value is converted into a digital value and input into a computer. The computer may obtain a value of an X-ray absorption coefficient of every point in a cross-section by high-speed calculation. The data of all the values of all the points may constitute an image matrix. Thereafter, the data may be shown with different gray levels through a display. As such, an anatomical structure of the cross-section can be clearly shown through a monitor. Alternately, a multiformat camera or a laser camera may be used to record the image on a photograph.
The X-ray source typically includes an X-ray tube which can emit X-ray under the drive of a tube current. When the X-ray tube is driven by a relatively large current, a clear image may be obtained. However, the human body is in turn exposed under a large radiation (namely, large radiation dose). Otherwise, when the X-ray tube is driven by a relatively small current, a serious image distortion may occur although the human body is exposed under a small radiation (namely, small radiation dose). Therefore, it is desired to obtain an image valuable to the diagnosis with the smallest radiation dose.
Currently, an ideal current modulation curve can be determined based on current modulation technology. Referring to FIG. 1, on the ideal current modulation curve, different expected current values can be determined according to different scanning angle. An image valuable to the diagnosis may be obtained with the X-ray tube driven under the determined expected current value with a smallest radiation dose.
However, referring to FIG. 1, it is found that there exists at least following issues in the current technology, an actual current value can not reach the determined expected current value due to an inherent limitation of the computed tomography imaging system, which in turn result in an image not valuable to the diagnosis with the smallest radiation dose.